1. Field of the Invention
The present invention relates to an information-acquiring device including an electronic-circuit body and a coil-shaped antenna inside a casing, and particularly relates to an information-acquiring device having improved transmission gain from the antenna.
2. Background Information
Inspecting and managing the air pressure of tires is important in conventional vehicles. Abnormal tire air pressure values often lead to accidents. Tire-state-monitoring systems are therefore well-known. In these tire-state-monitoring systems, a tire-information-acquiring device for detecting the air pressure within the tire of the wheel and for transmitting this information is provided to each of the wheels. The tire-state-monitoring systems are also provided with a monitoring device for acquiring the information about tire air pressure transmitted from the tire-information-acquiring device, monitoring the air pressure in the tires, and warning when the air pressure is abnormal (see, e.g., Japanese Patent No. 3962073).
The tire-information-acquiring device of the tire-state-monitoring system is positioned in an internal space formed between the tire and the wheel. The tire-information-acquiring device is configured so as to accommodate an air-pressure sensor, a transmitter, and the like in a casing. The air-pressure sensor is composed of a pressure-detecting element for detecting the air pressure within the tire, and the transmitter converts the detection results of the air-pressure sensor to an electrical signal and wirelessly transmits the signal to the monitoring device. A through-hole for guiding air in the internal space formed between the tire and the wheel to the internal air-pressure sensor is provided to the casing. The monitoring device is positioned near the driver's seat. The monitoring device receives the air-pressure information about the tires as transmitted from the tire-information-acquiring devices and produces a predetermined warning for the driver in cases where the air pressure in the tires is lower than a reference pressure that is set in advance.